Because printed circuit boards are becoming more complex, and are operating at ever-increasing speeds, the equipment for testing such boards is also becoming more complex and more expensive. Developments in test equipment which provide lower costs and better techniques are therefore most useful.
Printed circuit boards are customarily tested after component assembly is completed in order to find and remove any defects, whether they are related to manufacturing (such as solder shorts, copper shorts or wrong, misplaced or missing components), or whether the components were defective when purchased.
Board testing is customarily done by probing the board at strategic testing locations. The board can be stimulated through the probe points and can also be monitored through the probe points. In the past, it has frequently been necessary to wire wrap electrical connections from the probes to a receiver panel of the tester. This is costly, and also degrades the signals that are to be monitored, which hinders the test equipment from accurately evaluating the printed circuit board under test. Another difficulty which is sometimes found in connection with the use of test equipment is the build-up of static charges, particularly in the case of vacuum-operated test apparatus, to a sufficient level to alter test results, or even damage components of the printed circuit board. Another difficulty which has been found in the past is that of distortion of test signals caused by relatively long cable runs between the board under test and portions of the test apparatus, such as driver/sensor cards located inside of the tester.
One example of an apparatus for testing printed circuit boards which employs a plurality of probe assemblies is found in U.S. Pat. No. 4,551,675, filed Dec. 19, 1983, issued Nov. 5, 1985, inventors George Heys and Dennis R. Coon, assigned to the assignee of the present application.